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How do solids, liquids, and gases differ in shape and volume?

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Diagram showing four physical states of matter: solid with tightly packed molecules, liquid with loosely packed molecules, gas with widely spaced molecules, and plasma with free electrons and nuclei, each labeled with descriptions and an arrow indicating increasing energy. — phase States of matter.

The states of matter—solids, liquids, and gases—are distinguished by their macroscopic properties regarding shape and volume:

Solids: Possess both a definite shape and a definite volume. They maintain their structure when moved between containers and exhibit resistance to shear stress.123
Liquids: Retain a definite volume but lack a definite shape. They conform to the shape of the container in which they are placed and flow under external force.123
Gases: Have neither a definite shape nor a definite volume. They expand to completely fill any closed container, meaning their volume is determined by the container itself.12

These differences arise from the nature of atomic motion. In solids, atoms are not mobile and oscillate about fixed points, creating a durable structure. In liquids, atoms are mobile and wander throughout the material, allowing for flow. Gases consist of independent molecules that are relatively free of each other's influence, resulting in a lack of structure.312